PROJECT SUMMARY: Rhinovirus (RV) is the predominant cause of the common cold, a major contributor to virus-induced exacerbations of asthma, and infants who wheeze with RV infections are at increased risk for developing asthma. Of the three RV species (A, B and C), RV-C is a major contributor to wheezing illnesses and exacerbations of asthma in young children. In contrast to serologically characterized RV-A and B, current classification of RV-C is based solely on sequence identity in the VP1 region and whether these genotypes correspond to unique serotypes is unknown. Children with a single nucleotide polymorphism (SNP, rs6967330) in CDHR3 gene, encoding the cellular receptor for RV-C, are at greatest risk for RV-C infections and illnesses. This coding SNP is also a risk factor for early onset childhood asthma. There are no specific antivirals or vaccines for treatment and prevention of RV-C induced illnesses but vaccination to prevent RV infections (and particularly RV-C in young children with the CDHR3 SNP) could have major public health impact. Our recent studies in animal models have demonstrated the feasibility of polyvalent inactivated RV vaccine antigens. New discoveries related to RV- C structure, naturally-acquired immunity and human monoclonal antibody production will help us to fill existing knowledge gaps and develop RV-C vaccine approaches suitable for clinical trials. Little is known about the mechanisms of neutralizing antibody responses to RV-C. Neutralizing epitopes for RV-A and RV-B were mapped to the most prominent surface protrusions of capsid proteins. Interestingly, the first cryo-EM atomic structure of RV-C revealed unique, protruding ?finger-like? spikes, formed by VP1, predicted to be dominant immunogenic epitopes. We will test for type-specific and cross-reactive epitopes in these capsid structures. Another recent discovery is that humoral immunity to RV-C (compared to other RVs) is more rapidly acquired with age. We hypothesize that infections with RV-C can induce stronger, more cross-reactive neutralizing antibody responses of longer duration compared to RV-A, due to (i) their ability to induce more severe illnesses in young children, and (ii) some key structural and/or functional differences in major neutralizing immunogenic epitopes. To test this hypothesis, we propose three specific aims: 1) to identify host and viral determinants of neutralizing antibody responses combining the RV typing data from multiple cohort studies (n=14) and analysis of titers, time of appearance and duration of these antibody responses in the COAST children; 2) to determine whether RV-C genotypes represent unique serotypes or share common epitopes; 3) using human monoclonal antibodies complexed with RV-C, map major immunogenic epitopes and determine the mechanisms of RV-C antibody neutralization and cross-neutralization by cryo-EM. These studies will inform the development of a broadly protective RV-C vaccine that could be of significant benefit to young children at increased risk for RV-C induced lower respiratory tract infections.